Spike-time dependent plasticity (STDP) is a process that produces changes in the
synaptic strength. It is calculated taking into consideration the times between
the spikes of the postsynaptic neuron \(t_i\)  and the presynaptic neuron \(t_j\) .
The change in the excitatory synaptic weights \(\Delta g_{ij}\)  due to the time
difference \(\Delta t_{ij}=t_i-t_j\)  is given by
[1]}, [2]}, [3]}, [4]}
\(\Delta g_{ij}= \left\lbrace \begin{array}{ll}\displaystyle A_1{\rm e}^{(-\Delta t_{ij}/\tau _1)}\;\;\;,\;\;\; {\rm if} \;\;\;\Delta t_{ij} \ge 0\;\;\;\;\\\displaystyle -A_2{\rm e}^{({\Delta t_{ij}/\tau _2})}\;\;,\;\;\; {\rm if} \;\;\;\Delta t_{ij}<0 \\\end{array}  \right.\) 
